Magnetic properties of nanocrystalline γ'-Fe/sub 4/N and έ-Fe/sub 3/N synthesized by citrate route

Abstract

Nanocrystalline /spl gamma/'-Fe/sub 4/N and /spl epsi/-Fe/sub 3/N nitrides are synthesized by using a citrate precursor route. The nitridation of /spl alpha/-Fe/sub 2/O/sub 3/ results in a nitrogen deficient perovskite /spl gamma/'-Fe/sub 4/N phase at 773 K and hexagonal /spl epsi/-Fe/sub 3/N phase at 823 K. The nitride particle is a magnetic cluster consisting of an assembly of crystallites. /spl gamma/'-Fe/sub 4/N is a weak itinerant ferromagnet and the particles exhibit acicular platelet-like morphology. The magnetic moments in ultrafine /spl gamma/'-Fe/sub 4/N and /spl epsi/-Fe/sub 3/N nitride particles are due to spin pairing effects, lattice expansion due to interstitial nitrogens, superparamagnetic behavior, and randomly canted spin structures at the surface. The reduction of magnetization and Curie temperature (T/sub c/) is attributed to fine particle size effects. In /spl gamma/-Fe/sub 4/N and /spl epsi/-Fe/sub 3/N, the intermixing of N-2p states with Fe-3d states occurs because of similarities in their density of states, and thus the reduction of unpaired d-electrons results in the lowering of magnetic moments compared to /spl alpha/-Fe. The Mossbauer study of /spl gamma/'-Fe/sub 4/N and /spl epsi/-Fe/sub 3/N nitrides indicate randomly canted spin structures at the surface and corroborates the observed magnetic properties.